MEMS devices are becoming increasingly prevalent as new and additional applications are developed employing MEMS technology. In many applications, it is important that the manufacturing processes for forming the MEMS structure be compatible with integrated circuit manufacturing processes, particularly CMOS manufacturing processes. This is particularly so as, in many applications, MEMS devices are formed simultaneously with formation of CMOS devices, or at least formed on the substrate as CMOS devices.
Frequently, it is desirable to form deep trenches within the substrate on and in which a MEMS device is formed for various applications. One such application, for instance, is an ink head printer device in which ink flows through openings formed through the substrate.
FIG. 1a illustrates a conventional ink head MEMS device 1 at an intermediate stage of manufacture. As shown, substrate 2 has formed therein deep openings or trenches 4 which allow for the passage of fluids such as printing ink. In the stage of manufacture illustrated in FIG. 1, openings 4 are blind, meaning they do not open fully through substrate 2. At a later stage of manufacture, the back side of substrate 2 will be removed, e.g., through grinding, etch-back, or like process, to the level of openings 4. Conventionally, openings 4 are filled with a sacrificial material, typically a polymer such as a conventional photoresist during subsequent manufacturing process steps.
Formed at a top surface and a top substrate 2 are various elements and features of conventional CMOS devices, including doped regions within substrate 2, polysilicon gate lines, inter-layer dielectric (ILD) layers, inter-metal dielectric (IMD) layers, conductive interconnects, passivation layers, and the like as are well known in the art of CMOS processes. As the details of the CMOS devices are not necessary to understand the described embodiments, these elements and features are collectively illustrated as CMOS device layer 6. Openings 4 extend through CMOS device layer 6 as well.
Formed a top CMOS device layer 6 is a MEMS device layer 8, both of which are shown exaggerated in the illustration of FIG. 1a. MEMS device layer 8 could include a reservoir 9, which is in communication with openings 4.
Openings 4 communicate with reservoir 9 formed a top substrate 2, as is known in the art. Conventionally, openings 4 are filled with a sacrificial material, such as photoresist material or other polymer, in order to protect openings 4 during subsequent manufacturing steps. Photoresist material such as Novalic Resin, PMMA (poly-methylmethacrylate), PBS (poly-butene-1 sulfone), poly-vinylcinnamate, polysilane, an acrylic resin, Epoxy, a precursor of polyimide, and the like are commonly used in CMOS manufacturing processes and their properties and characteristics are well understood.
Typically, photoresist material is applied to the device and allowed to fill openings 4. Once the openings are filled, the photoresist material is cured. Curing changes the material properties of photoresist material and hardens the material making it effective for protecting openings 4 during subsequent processing steps. After subsequent processing steps, photoresist material can be readily removed using, for instance, oxygen plasma, ashing, or other well known techniques.
A disadvantage of the prior art is that photoresist material shrinks during the curing process. This shrinking places significant stress on surrounding substrate 2 and can cause substrate 2 to warp, as illustrated in exaggerated form in FIG. 1b. The warpage of substrate 2 complicates subsequent steps that require a planar surface, such as photolithography steps, and can significantly impede the performance or yield of the resulting device(s). The warpage illustrated in FIG. 1b is further exacerbated by the high temperature process steps, such as chemical vapor deposition (CVD) and sputter processes which occur in the manufacture of MEMS device layer 8. These high temperature process steps impact significant thermal energy unto substrate 2, which further contributes to the problems associated with warpage.
What is needed, then, is a manufacturing process that eliminates or reduces the warpage associated with conventional manufacturing processes.